Well, it's not Blood type related, but if I'm correct C's did left us with clue regarding physical appearance of "convergent" bloodline "member" which may be useful in putting the puzzles together.
From citation above it's clear that "bloodline" person could very likely be white skinned men/women with cleft chin and it may be that this characteristics are one of main designation of their "kind" so to speak.
Although this is not carved in stone, quote from same session:
Session980620
...
Q: Then, that makes me think that the significant thing that we are looking for is a convergence of the blood lines... These
lines are symbolized by the god figures, the children of Odin, and what we are looking for is a place where these lines
converge?
A: Yes.
Q: Well, what characteristics might an individual have that is a product of this convergence?
A: Fair skinned and cleft chin.
...
From citation above it's clear that "bloodline" person could very likely be white skinned men/women with cleft chin and it may be that this characteristics are one of main designation of their "kind" so to speak.
Although this is not carved in stone, quote from same session:
Q: Well, Ark and F**** both have cleft chins, but C**** and I don't! Does this mean...
A: We aren't saying that all with these features are of that blood line!
Q: So, you can have the bloodline and look quite different?
A: Yes.